Pirates of the Caribbean: On Stranger Tides is crashing into theaters, and already has its work cut out for it: the last three films in the franchise were profitable, although the third got mixed reviews compared to the first two. But if history is any indication, On Stranger Tides has more to overcome: the fourth film in a sci-fi series has a long tradition of bombing, sometimes so hard that it blows up the entire franchise . Here are 7 "fourth films" that brought their franchises to a new low. Batman & Robin Before Christopher Nolan took Batman to lofty heights with his series reboot, Batman was the star of several successful movies in the late 20th century. Batman, Batman Returns, and Batman Forever were received well both critically and at the box office, it was a no-brainer for Warner Bros. to commission a fourth film. Joel Schumacher was selected as director for his excellent work in Batman Forever. So everything looked like it was going smoothly. Warner Bro...